CPU hotplug, debug: detect imbalance between get_online_cpus() and put_online_cpus()

The synchronization between CPU hotplug readers and writers is achieved
by means of refcounting, safeguarded by the cpu_hotplug.lock.

get_online_cpus() increments the refcount, whereas put_online_cpus()
decrements it.  If we ever hit an imbalance between the two, we end up
compromising the guarantees of the hotplug synchronization i.e, for
example, an extra call to put_online_cpus() can end up allowing a
hotplug reader to execute concurrently with a hotplug writer.

So, add a WARN_ON() in put_online_cpus() to detect such cases where the
refcount can go negative, and also attempt to fix it up, so that we can
continue to run.

Change-Id: I144efeaa5899a2e8a3cddd21f010679cbaaa2459
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 075663d19885eb3738fd2d7dbdb8947e12563b68
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>
Signed-off-by: Dan Trifan <jimsth@gmail.com>
ARM: smp: fix incorrect per-cpu definition of regs_before_stop

The commit efd002896a3636a4d1606ac0630aaafbbfdea9aa introduced changes
to store CPU registers for all CPUs that handle IPI_CPU_STOP. The
structure to save the registers was intended to be a per-cpu variable.
However, the patch did not allocate a per-cpu structure and instead only
ended up providing a compiler per-cpu directive. Fix this bug by actually
defining a static per-cpu variable.

Change-Id: Ifd192223c135025897e10312f61b108757575068
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>
Signed-off-by: Dan Trifan <jimsth@gmail.com>
ARM: Flush the caches for non panicking CPUs in case of a kernel panic

In case of a kernel panic, only the panicking CPU does an entire
cache flush. This means that certain dirty cache lines in the L1
caches of the other CPUs may never get flushed. This gives us
improper RAM dumps. Add cache flushing for all the online CPUs.
The outer domain is not flushed since it is already being done by
the panicking CPU.

Change-Id: Ibf844ecf6b4dbc3c623789f72a26936aeb4a7306
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>
Signed-off-by: Dan Trifan <jimsth@gmail.com>